The publication “Towards the Multitrack Digital Video Tape Recording” by Francois Maurice in “The Magnetic Society of Japan” 1991, Volume 15, pages 389 to 394 discloses a magnetic tape recorder in which a large number of data and/or signal tracks are recorded on a magnetic tape using the method of longitudinal track recording. In the case of the apparatus disclosed in this document, the data tracks are written simultaneously by means of a matrix head. In one exemplary embodiment of this apparatus, up to 80 parallel tracks are written with a width of 7 μm without guard bands, that is to say without any intermediate space between the individual tracks.
The data tracks are read by a magneto-optical scanning device, which has a magneto-optical transducer. Using the Kerr effect, the alternating magnetization on the data tracks is converted into optical signals from which, in turn, electrical signals are produced by means of a photo-sensitive CCD element (“Charge Coupled Device”). In this case, each data track is assigned a cell or a pixel of the CCD element. In order to replay the stored data correctly, it is advantageous if each data track is imaged onto one, and only one, associated CCD pixel, to be precise even if, for example, the height of the magnetic tape is fluctuating or if mechanical vibration is varying the position of the data tracks with respect to the magneto-optical transducer. In order to achieve this aim, it is known from the prior art for a transparent plane-parallel tracking plate to be provided in the beam path between the magneto-optical transducer and the CCD element. The tracking plate is movable which means that one, and only one, data track is imaged onto each CCD pixel, as is disclosed, for example, in German Patent Application 197 47 493.4, from the same applicant.
In the case of a “Stationary Digital Cassette Recorder” magnetic tape system which is referred to by the abbreviation SDCR, 80 data tracks are recorded simultaneously, of which three are so-called servo tracks in which suitable patterns are stored in order to make it possible to detect a laterally offset map of the optical signals emitted from the magneto-optical transducer, on the CCD element. Suitable patterns and a method for evaluation of these patterns are described in German Patent Application DE-A 196 10 089 from the same applicant. However, these are not the subject of the present application.
The known method and the known appliance are able to compensate very quickly for fluctuations in the tape height and mechanical vibration. However, in practice, it has been found that the optics which are used are not always able to image all 80 data tracks completely homogeneously. This means that, for example, the first data tracks on one edge of the magnetic tape are imaged precisely onto one pixel, while a significant error occurs between the last data tracks on the other edge of the magnetic tape and their associated pixels.